BCL-X(L) OVEREXPRESSION RESTRICTS HEAT-INDUCED APOPTOSIS AND INFLUENCES HSP70, BCL-2, AND BAX PROTEIN-LEVELS IN FL5.12 CELLS

Although several proteins hare been identified that can inhibit stress -induced apoptosis, the cytoprotective potential of bcl-x(L) against h eat shock and its ability to alter hsp70 induction is not known. The c urrent study, using control and bcl-x(L)-overexpressing IL-3-dependent FL5.12 cells, compared the effects of 1 h of acute heat stress (42 de grees C) followed by 1, 4, and 8 h recovery (37 degrees C) on hsp70, b ax, bcl-2, and bcl-x(L) protein levels and apoptosis. Less than 0.5% o f untreated cells were apoptotic. There was significantly more apoptos is in control (similar to 16%) as compared to bcl-x(L) cells (similar to 3%) 8 h after heat stress. Immunoblotting revealed a time-dependent increase in hsp70 protein levels following 1 h of heat stress in cont rol, but not bcl-x(L)-overexpressing cells, bcl-2 protein levels were lower in bcl-x(L)-overexpressing cells than in controls, but decreased in both cell lines after heat stress. bax protein levels in bcl-x(L)- overexpressing cells were decreased similar to 80% below baseline leve ls 1 h post heat shock. This decrease was maintained to 8 h. No change in bax protein was observed in control cells up to 8 h post heat shoc k. These data indicate that bcl-x(L) overexpression mitigates the effe cts of acute heat stress so that hsp70 induction is eliminated and apo ptosis is prevented. The rapid loss of bax protein following heat stre ss in bcl-x(L)-overexpressing, but not control, cells mag contribute t o their resistance to apoptosis. Conversely, the loss of bcl-2 protein following heat stress in control cells may contribute to their suscep tibility to apoptosis. (C) 1997 Academic Press.